Gas pipe for exhaust gas recirculation

Abstract

A plurality of upper fins and a plurality of lower fins are each provided in an EGR passage so as to be adjacent to each other across a predetermined space in a direction perpendicular to an exhaust-gas flow direction. The upper fins and the lower fins are gradually narrowed in width toward their respective projection directions, so that both sides thereof in their width direction have inclined surfaces. A tilt angle of the inclined surfaces of the lower fins is made larger than a tilt angle of the inclined surfaces of the upper fins.

What is claimed is: 
     
       1. A gas pipe for sending exhaust gas discharged from an engine to an air-intake system of the engine, the gas pipe comprising:
 first fins; and 
 second fins, 
 the first fins and the second fins being configured such that:
 a) the first fins project from a first region of an inner peripheral surface of the gas pipe; 
 b) the second fins project from a second region of the inner peripheral surface of the gas pipe, the second region being opposed to the first region; 
 c) the second fins face the first fins across a predetermined space; 
 d) the first fins extend along an exhaust-gas flow direction; 
 e) the second fins extend along the exhaust-gas flow direction; 
 f) the first fins are adjacent to each other in a direction perpendicular to the exhaust-gas flow direction; 
 g) the second fins are adjacent to each other in the direction perpendicular to the exhaust-gas flow direction; 
 h) a thickness of the first fins in the direction perpendicular to the exhaust-gas flow direction is gradually thinned toward a projection direction of the first fins, so that oppositely facing sides of each of the first fins extending along the exhaust-gas flow direction define inclined surfaces; 
 i) a thickness of the second fins in the direction perpendicular to the exhaust-gas flow direction is gradually thinned toward a projection direction of the second fins, so that oppositely facing sides of each of the second fins extending along the exhaust-gas flow direction define inclined surfaces; and 
 j) a tilt angle of either ones of the inclined surfaces of the first fins and the inclined surfaces of the second fins is larger than a tilt angle of the other ones of the inclined surfaces of the first fins and the inclined surfaces of the second fins. 
 
 
     
     
       2. The gas pipe according to  claim 1 , wherein:
 the first fins project downward in a vertical direction; 
 the second fins project upward in the vertical direction; and 
 the tilt angle of the inclined surfaces of the second fins is larger than the tilt angle of the inclined surfaces of the first fins. 
 
     
     
       3. The gas pipe according to  claim 1 , wherein:
 the first fins project downward in a vertical direction; 
 the second fins project upward in the vertical direction; 
 the gas pipe includes an inlet portion for the exhaust gas, an outlet portion for the exhaust gas, and an intermediate portion between the inlet portion and the outlet portion; 
 the intermediate portion is lower than the inlet portion and the outlet portion in the vertical direction; 
 a height of the second fins at the intermediate portion is lower than a height of the second fins at the inlet portion and a height of the second fins at the outlet portion; and 
 tip portions of the second fins at the intermediate portion are set to a position lower than a central position in the gas pipe in a height direction of the gas pipe. 
 
     
     
       4. The gas pipe according to  claim 1 , wherein
 the gas pipe is provided inside a cylinder head.